Symptoms of abnormal heart rhythms are generally referred to as cardiac arrhythmias, with an abnormally rapid rhythm being referred to as a tachycardia. The present invention is concerned with the treatment of tachycardias, which are frequently caused by the presence of an "arrhythmogenic site" or "accessory atrioventricular pathway" close to the inner surface of the chambers of a heart. The heart includes a number of normal pathways, which are responsible for the propagation of electrical signals from the upper to lower chambers necessary for performing normal systole and diastole functions. The presence of arrhythmogenic site or accessory pathway can bypass or short circuit the normal pathway, potentially resulting in very rapid heart contractions, referred to here as tachycardias.
Treatment of tachycardias may be accomplished by a variety of approaches, including drugs, surgery, implantable pacemakers/defibrillators, and catheter ablation. While drugs may be the treatment of choice for many patients, they only mask the symptoms and do not cure the underlying causes. Implantable devices only correct the arrhythmia after it occurs. Surgical and catheter-based treatments, in contrast, will actually cure the problem, usually by ablating the abnormal arrhythmogenic tissue or accessory pathway responsible for the tachycardia. It is important for a physician to accurately steer the catheter to the exact site for ablation. Once at the site, it is important for a physician to control the emission of energy to ablate the tissue within the heart.
Of particular interest to the present invention are radiofrequency (RF) ablation protocols, which have been proven to be highly effective in tachycardia treatment while exposing a patient to minimal side effects and risks. RF catheter ablation is generally performed after conducting an initial mapping study where the locations of the arrhythmogenic site and/or accessory pathway are determined. After a mapping study, an ablation catheter is usually introduced to the target heart chamber and is manipulated so that the ablations tip electrode lies exactly at the target tissue site. RF energy or other suitable energy is then applied through the electrode to the cardiac tissue in order to ablate the tissue of arrhythmogenic site or the accessory pathway. By successfully destroying that tissue, the abnormal signal patterns responsible for the tachycardia may be eliminated.
The tip section of a catheter is referred to herein as the portion of that catheter shaft containing at least one electrode. In one embodiment, a catheter utilized in the endocardial mapping and/or RF ablation is inserted into a major vein or artery, usually in the neck or groin area. The catheter is then guided into an appropriate chamber of the heart by appropriate manipulation through the vein or artery. The tip of a catheter must be maneuverable by a physician from the proximal end of the catheter, so that the electrode means at the tip section can be positioned against the tissue site to be mapped or ablated. The catheter must have a great deal of flexibility in order to follow the pathway of major blood vessels into the heart. It must permit user manipulation of the tip even when the catheter body is in a curved and/or twisted configuration.
The tip section of a conventional electrophysiology catheter that is deflectable usually contains a plurality of electrodes in series. To accurately locate the electrodes inside a heart is not an easy task. The electrodes in series, such as those on a conventional tubular catheter or a loop catheter, can only provide signals information on a one-dimensional basis. The basket type catheter usually has the electrodes arranged in a contour or basket manner. The exact relative location of each electrode in a basket type catheter is distorted because of the effect of its curvature, especially when one side of the basket is compressed against the endocardial wall.
Therefore, there is an urgent clinical need to have a plurality of electrodes in a relatively flat plane so that the signal obtained from each electrode can be correlated and mapped accurately for future ablation operations. A plurality of electrodes on the lattices of a trellis fixture can provide the endocardial signals in a series of precise pre-determined relative coordinates for mapping assessment.